Common Channel Signaling System Number-7 ("CCS7" or "SS7") is a method of signaling that uses an out-of-band or separate channel signaling for conveying signaling information for a number of telecommunications channels. Common channel signaling is used in the Public Switched Telephone Network ("PSTN"), with Integrated Services Digital Network ("ISDN"), circuit switched networks and data networks. Common channel signaling is also being used for cellular and mobile telephony and network management.
The common channel carrying signaling information is called a signaling link. Signaling information is exchanged between signaling points over a signaling link using signaling data packets. Common channel signaling system number-7 includes a structured protocol partitioned into four levels including from lowest to highest a physical, data link, network and user part level. The physical, data link and network levels transfer signaling messages between signaling points reliably and accurately. They also provide network management functions. The physical, data link and network levels are collectively referred to as the Message Transfer Part ("MTP").
The user part level includes signaling applications to provide desired functionality. The user part level includes a Telephone User Part ("TUP"), ISDN User Part ("ISUP"), Transaction Capability Application Part ("TCAP") and others. The ISDN User Part includes both analog and digital telephony.
A common channel signaling gateway host is often used on Local Area Networks("LAN") to interface with the public switched telephone network. One of the functions of the common channel signaling gateway host is to convert a common channel signaling user part message (e.g., ISDN user part messages) into a local protocol that is known by network devices on the local area network. The local protocol messages arc forwarded over a local area network connection to network devices to set up a telecommunications connection.
For example, a common channel signaling host may convert a common channel signaling ISDN user part message into a local protocol message and send the local protocol message over a local area connection to a modem device to set up a telephone call or a data connection. The modem device will respond to the common channel signaling host in the local protocol. The common channel signaling host will then convert the local protocol response back to the common channel signaling protocol and send the response to the public switched telephone network to complete set up of the telephone call or data connection.
Using a common channel signaling gateway on a local area network is subject to several problems. If the local area connection between the common channel signaling gateway and the network devices (e.g., modem devices) fails, communications with the public switched telephone network may be lost unless there is a backup signaling path.
One solution is to provide a backup signaling path using an alternative connection to the local area network from the common channel signaling gateway. However, a hardware or software problem may exist that will also affect the alternative connection to the local area network. For example, if one or two ports on an Ethernet card are used to connect a local area network to a common channel signaling host, and the connection fails, an attempt may be made to use the second port on the Ethernet card as an alternative connection. However, the hardware or software on the Ethernet card may be defective and the alternative signaling connection may be lost. Another Ethernet card may also be used for the alternative connection. However, the Ethernet cards may have a common hardware or software problem so the alternative signaling connection may be lost again.
Thus, it is desirable to provide an alternative connection between a local area network and a common channel signaling gateway host. The alternative connection should not use the same network device to connect the local area network and the common channel signaling gateway host as is used for the primary connection to prevent a common hardware or software problem from affecting both the primary and alternative connection.